The present invention relates to the field of bridge rectifiers and, more particularly, the present invention relates to synchronous bridge rectifiers, methods of operating synchronous bridge rectifiers, and components thereof.
A bridge rectifier converts an alternating current (AC) signal to a direct current (DC) signal. This process is also referred to as “rectification.” Bridge rectifiers are commonly used in off-line power supplies that receive power from a sinusoidal AC power source and provide a voltage-regulated DC output that can be used to power a load, such as an electronic device. While such power supplies often perform subsequent processing and transformation on the rectified DC signal, a bridge rectifier performs an essential function of converting the AC signal to a DC signal.
FIG. 1 illustrates a bridge rectifier circuit of the prior art. As shown in FIG. 1, a first diode D1 has its cathode coupled to the cathode of a second diode D2. The anode of the second diode D2 is coupled to the cathode of a third diode D3. The anode of the third diode D3 is coupled to the anode of a fourth diode D4. The cathode of the fourth diode D4 is coupled to the anode of the first diode D1. The node between the anode of the first diode D1 and the cathode of the fourth diode D4 provides a first input terminal for the AC source, while the node between the anode of the second diode D2 and the cathode of the third diode D3 provides a second input terminal for the AC source. The node between the cathode of the first diode D1 and the cathode of the second diode D2 provides a first output terminal for the DC signal, while the node between the anode of the third diode D3 and the anode of the fourth diode D4 provides a second output terminal for the DC signal. An AC input signal VAC is applied across the input terminals to produce a rectified DC output signal VDC across the output terminals.
FIG. 2 illustrates the AC sine wave input signal VAC and the rectified DC output signal VDC. As shown in FIG. 2, the AC input signal VAC crosses above and below the zero volt level. The resulting pulsating DC output signal VDC remains above the zero volt level. The rectifier illustrated in FIGS. 1 and 2 is a full-wave rectifier, meaning that positive and negative portions of the AC input signal, above and below the zero volt level, are transformed to the output. Other types of rectifiers include half-wave rectifiers in which either the positive or negative half of the AC input is passed to the output, while the other half is blocked.
Use of diodes in the rectifier makes for a relatively simple design, however, the voltage drop across the diodes (approximately 0.7 volts), generates heat and diminishes efficiency. Therefore, what is needed is an improved bridge rectifier.